Refrigerating apparatus



June 8,1937. H; F. 'sMm-p RBFRIGERATING' APAR TUs Filed Oct. 31, 1933 INVENTOR HIS ATTORNEYS.

Patented June 8, 1937 v UNITED STATE REFRIGERATING APPARATUS Harry F. Smith, Dayton, Ohio,

assignor to Gen eral Motors Corporation, Daytom'Ohio, a corporation of Delaware.

Application October 31, 1933, Serial No. 695,981

Claims.

ticle with. a metal finish coat which coat will be isolated or electrolytically insulated from the metal employed to produce the article.

A more specific object of the invention is to prevent electrolytic action between a metallic member and a metal coating employed to cover or isolate the metallic member from exposure.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing, wherein a preferred form of the present invention is clearly shown.

In the drawing:

, Fig. 1 discloses a refrigerator cabinet having an evaporator constructed according to the present invention disposed in the cabinet and connected to a refrigerant liquefying and condensing unit shown diagrammatically;

Fig. 2 is a enlarged side elevational view of the evaporator shown in Fig. 1; and

Fig. 3 is anenlarged sectional view taken along the line 3-3 of Fig. 2 showing a portion of the evaporator constructed according to the invention.

The present invention is applicable to various metallic devices, articles or structures, wherein the base metal of such an article is desired to be electrically insulated or electrolytically isolated from a metal covering or coating provided on the article to eliminate or destroy their position relative to one another in the electro-chemical or displacement series so that no electrolytic action can occur between the metals. When I have herein described a specific article or product of manufacture for illustrating the application of the invention I wish it to be understood that I do not desire to be limited to this particular article or product. Therefore,-for the purpose of illustrating my invention, I hereinafter describe an article, device or product such as an evaporator of a refrigerating system, since my invention is particularly-useful or applicable to an article or device exposed to or upon which moisture accumulatcs'or collects and which moisture or water increases the likelihood of the occurrence of electrolytic action between twometals. However, application of the invention is equally important to products or devices merely exposed to atmosphere since the constituents of atmosphere cause corrosion of certain metals and electrolytic action between two adjacent metals of different compositions. My invention is also vto be distinguished from the idea of coating a base metal.

with a metal finish,-lower in the electro-chemical ordisplacement series relative to the base metal, so that the metal coating thereof instead I of the base metal is attacked and corroded or oxidized by air or moisture. The invention therefore distinguishes from the well known process of zinc plating iron or steel in the production of galvanized iron of which I am familiar, and therefore pertains to such articles which are desired tobe plated or coated with an easily applied metal such as tin or chromium, which will provide a hard finish that will remain in its original state without oxidization or discoloration indefinitely.

In present day manufacture of sheet metal evaporators of refrigerating systems-for example, a metallic sheet or sheets is or are corrugated in any suitable manner and secured together to provide a base metal of a unitary structure having refrigerant expansion passages therebetween. This unitary structure is then bent to form walls of a sharp freezing compartment for the evaporator. The base metal of such evaporators is ordinarily chosen from a group of metals different than the metal finish or coating applied to such evaporators. Known processes of plating one metal upon another have not been entirely satisfactory in that they do not always insure an impermeable coating over the base metal. For example, it has been found that small openings or pin holes, extending through the layer of metal plated upon a base metal, are often present after plating the one metal upon another. Since evaporators of refrigerating systems are usually maintained at low temperatures they cause condensation of moisture thereon in the form of a layer of frost or ice. An evaporator plated with a desirable exterior coating and having such openings or pin holes extending therethrough to the base metal thereof is not suitable for use over a long period of time due to certain chemical reactions which take place between the two metals, which action is caused by the constituents of air or moisture contacting the base metal and the coating metal. The occurrence of this reaction is due to the two metals and the water or moisture bridging the same and forming a battery, much like a Daniell cell as described'in many chemistry books, and in such battery the metal highest in the electrochemical series or displacement series is the one that is corroded. Since evaporators are often plated with a metal differing from the metal from which the evaporator is formed, one of the metals is acted upon and corroded or oxidizedeither by the oxygen inthe atmosphere or by metal in the production of evaporators which is in substantially the same range in the electrochemical or displacement series with the metal coating applied thereto or a metal having substantially the same properties as the coating metal. For example, manufacturers have been forming evaporators from sheets of brass, the cost of which is about seven or eight times that of other materials which might be employed for the purpose. The brass also presents complicated welding processes as compared to welding processes suitable for uniting or securing iron or steel plates together.

The brass has been plated with tin and rusting or corrosion of the brass due to exposure to atmosphere or to the electrolytic action hereinbefore described has been somewhat reduced or eliminated. However, the use of brass in addition to being very costly and complicated to weld has not entirely or positively eliminated the problem because corrosion will still occur with the use of brass and while the brass may not rust, it will oxidize and impair the appearance of the evaporator due to the presence of the oxide on the surface thereof. Therefore, since metals in substantially the same range in the electrochemical or displacement series are all quite expensive, the cost of producing sheet metal evaporators has been-high. Prior attempts to employ iron or steel as a base metal in the manufacture of evaporators or other articles, desired to have an everlasting metallic coat thereon, has not been satisfactory because the iron or steel not only rusts, corrodes and oxidizes, upon the occurrence of the chemical action referred to, upon the surface thereof but also continues to rust and corrode beneath the surface thereof until the metal is entirely disintegrated throughout its thickness.

Referring now to the drawing, I have shown in Fig. 1 thereof, for the purpose of illustrating the invention, an evaporator l0 constructed according to the present invention and installed in a refrigerator cabinet H. The evaporator, of course, includes the usual refrigerant expansion passages which are connected to a refrigerant liquefying and condensing unit, diagrammatically represented in the drawing, by conduits or pipes l2 and i3. Such a refrigerant liquefying and condensing unit is ordinarily contained in Y a compartment provided for the same in the refrigerator cabinet and in the present showing thisunit includes a compressor 55 which withdraws vaporized refrigerant from the cooling unit or evaporator it through the gaseous refrigerant return pipe or conduit E2. The vaporized refrigerant is compressed by the compres or iii and forced into a condenser it where it is condensed or liquefied in any suitable manner and caused to flow into a receiver if. The flow of the liquefied refrigerant from the receiver ll through the liquid line it to the evaporator it may be controlled in any of a plurality of different methods well-known to those skilled in the art. A motor 20 is operatively connected through a belt and pulley arrangement-2i, 22 and 23 to the compressor Is for driving the same. A switch 25 is interposed in the electric circuit leading to the motor 20 and this switch controls the starting and stopping operations of the motor and consequently the compressor 15. Switch 25 may be actuated in response' to the temperature of the evaporator I 0 by securing a thermostat 26 thereto I sheet is corrugated in any suitable manner asat 33 and folded upon itself and has contiguous portions thereof secured together such as by welding between the corrugations to provide a unitary structure having refrigerant expansion passages 34 formed therebetween, which passages communicate with the conduits l2 and I3. The unitary structure is then bent to the shape of the evaporator desired and preferably to a shape to provide the evaporator with a sharp freezing cornpartment for the reception of trays or the like. In the use of two sheets of iron or steel in the production of the evaporator, one of the sheets may be corrugated as explained and superimposed upon and secured to the other sheet to provide a unitary structure. This unitary structure is also then bent to the desired shape. The exterior surfaces of the evaporator formed from the iron or steel sheets 3! and 32 are then coated with a thin layer of clear baking lacquer, a quick drying oil, an asphaltic substance such as hydrolene, indicated at 36 in Fig. 3, to provide an impermeable film or coating over the exposed exterior surfaces of the iron or steel. This coating 36 forms a thin electrical insulating layer over the iron or steel and it may be applied thereto by dipping the evaporator into the substance or by spraying the substance thereon or in any other desired manner so long as a perfect impermeable film of the same is provided over the surfaces of the evaporator. The impermeable film over the steel or iron thus serves to electrolytically isolate this metal from another metal coat to be applied to the evaporator. Some suitable substance must then be applied to the impermeable coating in order to permit a metal to be electroplated on this coating. I, therefore, spray a suitable water solution of graphite, that is, a

solution having graphitesuspended therein upon the impermeable coating or I dip the evaporator into such a solution. The liquid of the solution is adapted to dry quickly, .thus leaving a thin coating of graphite 37 disposed on the impermeable coating material. Since graphite is a very good conductor of electricity, its thin coating on the insulating film thus permits the application to the surfaces of the evaporator of a primary metal coat such as copper or the like which is electrolytically disposed upon the surfaces of the evaporator and indicated at 38 in Fig. 3.

I have also found that powdered copper, iron or other suitable metals may be applied to the impermeable insulating coat and I may prefer the use of a metallic powder over graphite because the powdered metal can be blown, pressed or brushed into the outer surface of the insulating coat, thus forming a better adhesion to or bond with the insulating coat than by dipping the evaporator into a solution containing graphite, since graphite is slippery and has very little adhesive properties. The copper or iron is also a good conductor of electricity and the depositing of a primary coat of copper electrolytithe displacement-series than thebase: metal by cally upon powdered metal causes the primary copper coat to be more permanently secured to the evaporator upon being united with the powdered coat, which enters or roughens the surface of the insulating coat and thereby adheres thereto. Since the powdered metal enters the insulating coat and tends to bond therewith or adhere thereto, peeling of the metallic coat or finish, upon denting or scratching thereof, from the evaporator is prevented. After the metallic'coat of copper has been applied, any desired finish or decorative metal coat, indicated at 39 in Fig. 3, such as tin or chromium is then applied to the copper coat in any suitable manner such as by electroplating the same thereon for improving the appearance of the evaporator. Either a chromium or tin coat provides a bright shiny exterior finishjor the evaporator, which finish will not be discolored noroxidized by exposure 'to atmosphere or moistureand which surface may be readily cleaned even by cleaning mixtures containing certain acids without danger of impairing its neat appearance.

It. is to be understood that the impermeable coating is to be very thin, suflicient to electrically insulate or electrolytically isolate the base metal, iron or steel, of the evaporator from the coating or finish metal applied to the evaporator and that this layer or film of isolating material may be of a somewhat good thermal'conductor so as not to impair or impede the transfer or conduction of heat from a medium to be cooled by the evaporator to the surfaces thereof and to the reirigerant contained therein. It is to be also understood that the thin impermeable layer or film prevents contact of water ormoisture with ,ings or pin holes present in the metal exterior coatings applied to the evaporator.

In eliminating the occurrence of electrolytic action as described, I render iron or steel. suitable for use in producing articles, which articles wereheretofore necessarily constructed of a much more expensive metal. I have thus not only reduced the cost of such articles by the use of less expensive metal but have also greatly reduced the cost of and facilitated processes of manufacturing the article. Iron or steel has more de-- sirable properties and characteristics than brass and some other metals, in that in the production of an article wherein the article must be welded the iron or steel is more practical; since: it readily withstands-high temperatures and can: be welded. at a plurality'oiispots'without burning: the metal to forma certain structure.

It is apparent therefore that I have discovered? a novel method of coating or platingran evapoa rator and that I have provided improved evaporator which may: be constructedf of a metaii of low cost and plated or coated with: a". metal suitable of retaining its: bright. onlustrous: finish over long periods of. time withoutdiscoloratiom or. oxidation. It is also apparent have provided an evaporator which. may Deconstructed; of' a base metal of high. ranlc in-theelectrochemical displacement series and. coated or plated; with: a metal which is in a similar position. on lower: in

preventing electrolytic actions causedi by water ormoisture contacting the two.v metals: the evaporator minute openings which. arenot readily detected in the manufacture of the I evaporators. My invention not only prevents rusting, corroding, etc., of the surface of the base metal of the evaporator, but also prevents the entire thickness of the metal from being disintegrated and thereby becoming ineffective as a closed wall of a fluid passage. The advantages derived from my invention are twofold in that I prevent corrosion of the base metal. of the evaporator by isolating the same from atmosphere and also prevent electrolytic action between the base metal and a metallic coating placed thereover. This latter advantage may of course be accomplished without the necessity of providing a metal exterior finish but I have hereinbefore pointed out that the present invention is particularly applicable to such articles dematerial interposed between said container and.

said coating for electrically isolating the container from the metallic coating, said layer of insulating-material being of such character as to offer inappreciable resistance to the transfer of heat.

, 2. An evaporator for a refrigeratingsystem, a coating of electric-insulating material thereon adapted to insulate said evaporator without substantial interference with heat transference thereto, and a metallic coating over said insulating material, electrolytic action between said evaporator and said metallic coating being prevented by said electric insulating material.

3. An evaporator for; a refrigerating system comprising a container for refrigerant having a chromium coating therefor, a. layer of insulating material interposed between said container and said coating for electrolytically isolating the container from the coating; said layer of insulating material being of such character as to offer inappreciable resistance to the transfer of heat. 4'..An evaporator for; a refrigerating system comprising a container for refrigerant having a tin". coating. therefor, a layer ofinsulating material' interposed between said container and said coating for electrolytically isolating the container from the coating,said layer-of insulating material being of such characterrastdoifer inappreciable resistance to the transfer of heat;

Anv evaporator for a refrigerating. system comprising ametallic-memberhaving a first coating. thereon completely" enclosing the same, an electro-conductive coating supe s d. on said first coating, and: a metallic coating electro-deupon. said electro-conductivecoating providing a non-corrodible metal flnishfor said memberisolated'. therefrom, said first coating beingso-madeasto-constitute an electrolytic insulation hetweenthe member andthe metallic coat-. 

